Thermoplastic resins, when fabricated into articles, such as pipes, tank liners, containers, and the like usually contain a small amount of one or more additives, such as anti-oxidants, plasticizers, ultraviolet stabilizers, or heat stabilizers. It is believed that the additives normally do not undergo any reaction with the resin, but exist in the resin matrix as a separate phase.
It has been found that when thermoplastic resin articles are exposed to a fluid, particularly a heated fluid under pressure, such as hot water, the additives tend to be leached out of the resin, with the result that the additive is quickly depleted and the service life of the resin article is severely shortened.